Electronic devices, such as computer equipment, may contain power supplies that are used to convert AC input to DC output. When such power supplies are first turned on, there may be a significant and potentially harmful (e.g., to components of the power supply) inrush of current. One way to protect against such potentially harmful inrushes of current is to place a resistor in line with the AC input to limit the inrush of current.
Such resistors will also dissipate power and thus generate a small amount of heat during normal operation. However, if abnormal operation occurs, such as the power supply drawing excessive current due to a short circuit, excessive heat may be generated in the resistor. Such heat may, for example, deform a housing of the resistor, a housing of the power supply, and/or damage other components proximate to the resistor. Such heat may, for example, cause a resistive element of the resistor (e.g., the wire in a wire wound resistor) to melt. Such melting may disconnect the power supply from the AC input. Such melting may occur, for example, at temperatures on the order of 1000° C. and result in the deformation of the housing of the resistor and/or a housing of the power supply, sparks, flames, the leaving of exposed components attached to the AC input, and/or other undesirable conditions.
One known solution is to place a thermal fuse in series with and adjacent to the resistor such that as the resistor heats, the heat is transferred to the thermal fuse. If the heat reaches a certain level, the thermal fuse is tripped, opening the circuit and preventing continued heating of the resistor, thus avoiding undesired heat, flames, sparks, melting insulation, exposed conductors, etc. However, such a system requires precise placement of the components. If the thermal fuse is too far from the resistor, the fuse may not trip at the desired temperature, possibly leading to unsafe failure of the resistor. If the thermal fuse is too close, the fuse may trip prematurely.